Zooming In On Genetic Shuffling

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Zooming In On Genetic Shuffling

http://www.medicalnewstoday.com/articles/114727.php

Genetic recombination, the process by which sexually reproducing

organisms shuffle their genetic material when producing germ cells,

leads to offspring with a new genetic make-up and influences the

course of evolution. In the current issue of Nature, researchers at

the European Molecular Biology Laboratory (EMBL) in Heidelberg,

Germany, and the EMBL-European Bioinformatics Institute (EMBL-EBI) in

Hinxton, UK, present the most precise map of genetic recombination

yet. The study sheds light on fundamental questions about genetic

shuffling and has implications for the tracking of disease genes and

their inheritance.

In order to generate germ cells, sexually reproducing organisms

undergo a complex series of cell divisions (meiosis) that includes

the shuffling of genetic material inherited from the two parents.

Equivalent chromosomes from mother and father pair up and exchange

sections of DNA in a process called crossover. In a different type of

recombination, called non-crossover, a small piece of DNA is copied

from one chromosome onto the other without reciprocal exchange

leading to gene conversion. Non-crossovers are minute events with a

subtler effect than the exchange of larger fragments, but both types

of recombination can increase genetic diversity and explain why

organisms of the same species differ in many ways. Both types of

recombination can also act to separate the transmission of

neighbouring genes, which are normally inherited together.

The groups of Lars Steinmetz at EMBL and Wolfgang Huber at EMBL-EBI

have produced the most detailed map to date of recombination events

in the yeast genome.

" Our map has the highest resolution of recombination events that

currently exists for any organism. We can locate crossovers and even

hard-to-trace non-crossovers, typically with a precision of about 80

bases. This resolution is 20 times higher than in any existing yeast

map and more than 360 times higher than a recent human map, " says

Steinmetz.

The map revealed many new insights into the organisation of

recombination in yeast. On average over 150 recombination events were

observed during a typical meiosis. These events did not occur

uniformly across the genome. The recombination rate varied according

to location, with events concentrated at so-called hotspots, some of

which favoured either crossovers or non-crossovers. The researchers

also found evidence for interference between crossovers and non-

crossovers - a phenomenon previously only known to occur between

crossovers - that makes it unlikely for two recombination events to

happen in close proximity.

The fundamental principles of recombination are likely to be shared

between yeast and humans. " Our map expands our understanding of

crossover and provides a wealth of new information about non-

crossovers and gene conversion. It will act as a reference for future

research into recombination, " says Bourgon from Huber's

group, who developed the statistical methodology for this new type of

data.

The insights gained will not only help tackle questions about the

basic mechanisms of recombination; they will also have practical

implications for the tracking of disease genes in humans.